Blood oxygen saturation, herein oxygen saturation is a measurement corresponding to the degree to which the hemoglobin molecule is saturated with oxygen. Oxygen saturation provides a wealth of information about a patient's health including particular conditions. It can, for example, provide information on a person's pulmonary function, cardiovascular function, circulation and hematologic state. The current standard method for measurement of oxygen saturation is a technique known as oximetry. Oximetry is based on the principle that the color of blood is related to the oxygen saturation level (SaO2) in the blood. Oximetric devices use a light source and light dectector. Light from the light source (known as afferent light) is emitted into the patient's blood directly via a catheter or indirectly via a transcutaneous probe placed on the skin. Typically, the light source emits at least two separate wavelengths of light with each wavelength having different absorption curves such that the ratio of the two absorptions is unique for the range of oxygen saturations from 0% through 100% saturation. The detector detects light that is transmitted through the patient's blood known as efferent light. As is explained in more detail below, the nature of the efferent light depends on the blood oxygen saturation sated of the patient's blood. The efferent light can be collected directly from a catheter positioned in the patient's vasculature or indirectly via a transcutaneous probe. Information from the detector can then be sent to a processor which includes software for analyzing the afferent and efferent light in order to determine the level of oxygen contained in the patient's blood. More specifically, the software contains routines for analyzing the ratio of absorbances of the two emitted wavelengths and then determining blood oxygen saturation based on that ratio.
Current oximetry devices include probes that are placed on the skin or catheters that are placed in an artery such as the pulmonary artery. However both of the devices are unable to provide an indication of what the localized oxygen saturation is at a tissue site beneath the skin (other than the finger tip). Rather, they only provide an indication of what the systemic blood oxygen saturation is. Localized blood oxygen saturation for tissue sites beneath the skin can be used to diagnose a number of conditions including any number of conditions causing localized ischemia such as deep vein thrombosis, peripheral vascular occlusion, edema and cancer. What is needed is a device and method for measuring blood oxygen saturation at a localized level at a selected tissue site to facilitate diagnose of these and other diseases and conditions.
Also, current oximetric devices cannot be left in place for any extended period of time due to the requirement of having an in dwelling catheter or having a finger probe attached to the oximeter. What is also needed is an oximetric measurement device which can be left within the patient for an extended period without requiring the patient to be bedridden or otherwise tethered to an instrument.